Mechanism of oxalate decarboxylase Oxd_S12 from Bacillus velezensis BvZ45-1 in defense against cotton verticillium wilt

Abstract

Verticillium wilt, a soilborne vascular disease caused by Verticillium dahliae, strongly affects cotton yield and quality. In this study, an isolated rhizosphere bacterium, designated Bacillus velezensis BvZ45-1, exhibited greater than 46% biocontrol efficacy against cotton verticillium wilt under greenhouse and field conditions. Moreover, through crude protein extraction and mass spectrometry analysis, we found many antifungal compounds present in the crude protein extract of BvZ45-1. The purified oxalate decarboxylase Odx_S12 from BvZ45-1 inhibited the growth of V. dahliae Vd080 by reducing the spore yield, causing mycelia to rupture, and causing spore morphology changes, cell membrane rupture and cell death. Subsequently, overexpression of Odx_S12 in Arabidopsis significantly improved plant resistance to V. dahliae. Through studies of the resistance mechanism of Odx_S12, V. dahliae was shown to produce oxalic acid (OA), which has a toxic effect on Arabidopsis leaves. Odx_S12 overexpression reduced Arabidopsis OA content, enhanced tolerance to OA, and improved resistance to verticillium wilt. Transcriptome analysis and quantitative real-time PCR (qRT-PCR) analysis revealed that Odx_S12 promoted the outbreak of reactive oxygen species (ROS) and a salicylic acid (SA) and abscisic acid (ABA) mediated defense response in Arabidopsis. In summary, this study not only identified B. velezensis BvZ45-1 as an efficient biological control agent, but also identified the resistance gene Odx_S12 as a candidate for cotton breeding against verticillium wilt.

Keywords: Bacillus velezensis; Verticillium dahliae; biological control; oxalate decarboxylase; resistance gene; upland cotton.